Name:	rock_CashPaidToSettleLiabilityAwardsTableTextBlock
Namespace Prefix:	rock_
Data Type:	nonnum:textBlockItemType
Balance Type:	na
Period Type:	duration

Schedule of compensation expense recognized from change in fair value and vesting of performance stock units [Table text block].

No definition available.

Name:	rock_ScheduleOfCompensationExpenseRecognizedFromChangeInFairValueAndVestingOfPerformanceStockUnitsTableTextBlock
Namespace Prefix:	rock_
Data Type:	nonnum:textBlockItemType
Balance Type:	na
Period Type:	duration

Disclosure of the intrinsic value of options exercised and fair value of restricted stock and restricted stock units vested during the period.

No definition available.

Name:	rock_ScheduleOfFairValueOfOptionsExercisedAndOtherAwardsVestedTableTextBlock
Namespace Prefix:	rock_
Data Type:	nonnum:textBlockItemType
Balance Type:	na
Period Type:	duration

Tabular disclosure of components of a stock option or other award plan under which equity-based compensation is awarded to employees, typically comprised of the amount of unearned compensation (deferred compensation cost), compensation expense, and changes in the quantity and fair value of the shares (or other type of equity) granted, exercised, forfeited, and issued and outstanding pertaining to that plan. Disclosure may also include nature and general terms of such arrangements that existed during the period and potential effects of those arrangements on shareholders, effect of compensation cost arising from equity-based payment arrangements on the income statement, method of estimating the fair value of the goods or services received, or the fair value of the equity instruments granted, during the period, cash flow effects resulting from equity-based payment arrangements and, for registrants that accelerate vesting of out of the money share options, reasons for the decision to accelerate.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph 64, 65, A240

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5047-113901

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

Name:	us-gaap_DisclosureOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTextBlock
Namespace Prefix:	us-gaap_
Data Type:	nonnum:textBlockItemType
Balance Type:	na
Period Type:	duration

Disclosure of the number and weighted-average grant date fair value for restricted stock and restricted stock units that were outstanding at the beginning and end of the year, and the number of restricted stock and restricted stock units that were granted, vested, or forfeited during the year.

No definition available.

Name:	us-gaap_ScheduleOfSharebasedCompensationRestrictedStockAndRestrictedStockUnitsActivityTableTextBlock
Namespace Prefix:	us-gaap_
Data Type:	nonnum:textBlockItemType
Balance Type:	na
Period Type:	duration

Tabular disclosure of the number and weighted-average exercise prices (or conversion ratios) for share options (or share units) that were outstanding at the beginning and end of the year, vested and expected to vest, exercisable or convertible at the end of the year, and the number of share options or share units that were granted, exercised or converted, forfeited, and expired during the year.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Topic 718

-SubTopic 10

-Publisher FASB

-Number

-Article

-Subparagraph (c)(1)

-Name Accounting Standards Codification

-Paragraph 2

-Section 50

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

Name:	us-gaap_ScheduleOfShareBasedCompensationStockOptionsActivityTableTextBlock
Namespace Prefix:	us-gaap_
Data Type:	nonnum:textBlockItemType
Balance Type:	na
Period Type:	duration

Tabular disclosure of the significant assumptions used during the year to estimate the fair value of stock options, including, but not limited to: (a) expected term of share options and similar instruments, (b) expected volatility of the entity's shares, (c) expected dividends, (d) risk-free rate(s), and (e) discount for post-vesting restrictions.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Topic 718

-SubTopic 10

-Publisher FASB

-Number

-Article

-Subparagraph (f)(2)

-Name Accounting Standards Codification

-Paragraph 2

-Section 50

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

Name:	us-gaap_ScheduleOfShareBasedPaymentAwardStockOptionsValuationAssumptionsTableTextBlock
Namespace Prefix:	us-gaap_
Data Type:	nonnum:textBlockItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_ShareBasedCompensationAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Tabular disclosure of the weighted-average grant-date fair value of equity options or other equity instruments granted during the year.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Topic 718

-SubTopic 10

-Publisher FASB

-Number

-Article

-Subparagraph (d)(1)

-Name Accounting Standards Codification

-Paragraph 2

-Section 50

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValueTableTextBlock
Namespace Prefix:	us-gaap_
Data Type:	nonnum:textBlockItemType
Balance Type:	na
Period Type:	duration

Tabular disclosure of the number of fully vested share options (or share units) and share options expected to vest at the date of the latest statement of financial position, weighted-average exercise price (or conversion ratio), aggregate intrinsic value (except for nonpublic entities), and weighted-average remaining contractual term for both options (or share units) currently outstanding and options (or share units) exercisable (or convertible).

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Topic 718

-SubTopic 10

-Publisher FASB

-Number

-Article

-Subparagraph (e)

-Name Accounting Standards Codification

-Paragraph 2

-Section 50

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901